首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   43966篇
  免费   2556篇
  国内免费   170篇
耳鼻咽喉   550篇
儿科学   1212篇
妇产科学   852篇
基础医学   6257篇
口腔科学   4048篇
临床医学   3423篇
内科学   8985篇
皮肤病学   925篇
神经病学   3210篇
特种医学   917篇
外国民族医学   4篇
外科学   4724篇
综合类   487篇
一般理论   11篇
预防医学   5368篇
眼科学   577篇
药学   3073篇
中国医学   403篇
肿瘤学   1666篇
  2023年   382篇
  2022年   961篇
  2021年   1554篇
  2020年   1073篇
  2019年   1325篇
  2018年   1583篇
  2017年   1163篇
  2016年   1234篇
  2015年   1449篇
  2014年   1909篇
  2013年   2269篇
  2012年   3436篇
  2011年   3754篇
  2010年   1984篇
  2009年   1489篇
  2008年   2554篇
  2007年   2524篇
  2006年   2200篇
  2005年   1886篇
  2004年   1657篇
  2003年   1507篇
  2002年   1336篇
  2001年   849篇
  2000年   911篇
  1999年   736篇
  1998年   270篇
  1997年   186篇
  1996年   171篇
  1995年   148篇
  1994年   141篇
  1993年   112篇
  1992年   339篇
  1991年   305篇
  1990年   303篇
  1989年   285篇
  1988年   261篇
  1987年   199篇
  1986年   202篇
  1985年   200篇
  1984年   153篇
  1983年   118篇
  1979年   122篇
  1978年   107篇
  1975年   82篇
  1974年   84篇
  1973年   98篇
  1970年   98篇
  1969年   99篇
  1968年   87篇
  1967年   91篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
We investigated the cytokine profile of cells of the innate immune response and its association with active (ACT), asymptomatic (AS) and cured (CUR) human visceral leishmaniasis (VL), as well as noninfected (NI) subjects. The frequency of cytokine-producing cells was determined after short-term in vitro incubation of whole peripheral blood samples with soluble Leishmania antigen (SLA). Our data demonstrated a predominant type 2 cytokine profile in NI and ACT. In NI, we observed an increase of IL-4+ neutrophils, IL-10+ eosinophils besides a decrease of tumour necrosis factor (TNF)-alpha+ eosinophils/monocytes. Yet in ACT, we observed an increase of IL-4+ neutrophils and natural killer (NK) cells and IL-10+ monocytes, a reduced frequency of IL-12+ and IFN-gamma+ eosinophils and lower levels of TNF-alpha+ and IL-12+ monocytes. AS presented a mixed profile, characterized by an increase of IFN-gamma+ neutrophils/eosinophils and NK cells, of IL-12+ eosinophils/monocytes, as well as increase of IL-4+ neutrophils and NK cells and IL-10+ eosinophils/monocytes. In contrast, CUR was characterized by a type 1 response with an increase of IFN-gamma+ neutrophils/eosinophils and NK cells, associated with an increase in IL-12+ monocytes. In conclusion, we show a correlation between innate immune cytokine patterns and clinical status of VL, suggesting that these cells, in addition to other factors, may contribute to the cytokine microenvironment in which Leishmania-specific T cells are primed and to disease outcome.  相似文献   
142.
Quercetin has been the subject of numerous studies on its genetictoxicity and carcinogenicity. Despite its well-proven geneticdamaging activity for various genetic end-points (reverse mutations,induction of SOS functions, induction of sister chromatid exchanges,chromosomal aberrations and micronuclei), the mechanisms ofgenetic damage by quercetin remain, by and large, unknown. Thepresent study aims to further extend the observations on thepossible active oxygen species mediated DNA-damaging activityof quercetin and the role of cytochrome P450-dependent metabolismon the genotoxicity of quercetin. The results reported in thiswork show that querceitn can produce the OH radical, as assessedby deoxyribose degradation in the presence of Fe/EDTA(ethylenediaminetetraacetic acid), and that it induces strandbreakage in isolated plasmidic DNA (pUC18). The data supportthe hypothesis that the production of OH is mediated by H2O2.The results with genetically engineered V79 cells expressingrat cytochromes 1A1, 1A2 and 2B1 failed to demonstrate metabolismof quercetin, as indicated by the fact that neither an enhancementnor a decrease in the genotoxicity of quercetin was observed.Results obtained on the pH dependence of the induction of chromosomalaberrations by quercetin in V79 cells show that, as the valueof the medium is increased to 8.0, there is a significant increasein the number of aberrant cells, as expected if oxygen radicalsare responsible for the formation of chromosomal aberrations. 3To whom correspondence should be addressed  相似文献   
143.
We assayed natural killer (NK) cell activity and phenotype from human bone marrow (BM) following "purge" with 4-hydroperoxycyclophosphamide (4HC) at 60 micrograms/ml for 30 min in vitro. In all cases studied, lytic activity against the K562 cell line was either significantly decreased or abolished following 4HC purge. Although NK activity was significantly affected by 4HC treatment, no major differences in the phenotype between the purged and unpurged population were seen. Further, while in vitro culture of BM with IL2 resulted in a significant increment of NK activity, no IL-2 responsive cells were found in the 4HC purged BM after 14 days of culture. This study demonstrates that pharmacological purging of bone marrow results in a persistent functional decline of NK cell activity and may serve as a useful model for the study of the ontogeny of NK cells.  相似文献   
144.
Primary small cell (oat cell) carcinoma of the trachea is very rare. We report a case with ultrastructural evidence of endocrine differentiation. Immunoperoxidase staining demonstrated carcinoembryonic antigen and bombesin in the tumor cells.  相似文献   
145.
The isthmo-optic nuclei (ION) and ectopic neurons, which constitute the centrifugal visual system (CVS), are thought to be cholinoceptive and nitrergic. However, it is not clear which neurons express these markers, namely the ones that project to the retina rather than in neurons that only participate in a local circuit. Therefore, to characterize the neurochemical patterns of the centrifugal visual system in the post-hatched chick, retinopetal cells of the isthmo-optic nuclei and the ectopic region were identified via immunolabeling for cholera toxin, a neuronal tracer, which has been injected in the ocular globe. Then, double labeled with acetylcholinesterase histochemistry to reveal cholinergic synapses, or NADPH-diaphorase histochemistry as a nitrergic marker. Briefly, acetylcholinesterase activity was present mainly in cholera toxin labeled cell bodies of the isthmo-optic nucleus and the ectopic region indicating that retinal projecting neurons of centrifugal visual system comprise a cholinoceptive pathway. On the other hand, NADPH-diaphorase histochemistry was present in the neuropile and sparse cell bodies inside of the isthmo-optic nucleus and in ectopic neurons which were not cholera toxin positive suggesting their role in an intrinsic circuit of the centrifugal visual system. These data support the idea that these two neurochemical systems are present in distinct neuronal populations in the centrifugal visual system.  相似文献   
146.
Rats bearing lesions in the septal area followed by lesions in the subfornical organ were submitted to various thirst-eliciting procedures. The rats with hyperdipsia induced by lesions of the septal area drank more water than either during the control period or after lesion of the subfornical organ under the same thirst-eliciting or angiotensin-liberating stimuli (polyethyleneglycol, isoproterenol, water deprivation and ligation of the inferior vena cava). The overdrinking elicited by lesions in the septal area was blocked after lesion of the subfornical organ. Neither hypovolemia, nor hypotension or water deprivation could elicit increased water intake in animals whose subfornical organ had been destroyed. Animals with lesions in the subfornical organ showed decreased water intake after cellular dehydration. The results obtained suggest that the subfornical organ acts as a more important structure than the septal area in the regulation of water intake elicited by angiotensin, with two opposite effects: a direct one facilitating water intake, and an indirect one inhibiting the septal area. The septal area has an inhibitory effect on the subfornical organ and on water intake.  相似文献   
147.
Quality of Life Research - Neck pain tends to persist for periods of 1 to 4 years of follow-up in adolescents, and a high percentage of them report disability. However, studies assessing...  相似文献   
148.
Maternal and Child Health Journal - Dietary patterns can influence maternal and child health outcomes. The study aims to characterize dietary patterns during pregnancy as well as to identify their...  相似文献   
149.
During the COVID-19 pandemic, breastfeeding women have experienced restricted access to support, placing them at increased risk of mental health concerns and limited breastfeeding assistance. This study investigated the effect of the pandemic on feeding choices and maternal wellbeing amongst breastfeeding mothers living in Australian and New Zealand. We conducted a cross-sectional online survey that examined feeding methods, maternal mental wellbeing, worries, challenges, and positive experiences during the pandemic. Most women were exclusively breastfeeding (82%). Partial breastfeeding was associated with perceived low milk supply and longer pregnancy duration during the pandemic. Reduced mental health and wellbeing was associated with lower levels of family functioning, increased perceived stress, and perinatal anxiety. Longer pregnancy duration during the pandemic was associated with lower mental health wellbeing scores, while higher perceived stress scores were reported for regions with higher COVID-19 infection rates and women with perceived low milk supply. Women reported that the pandemic resulted in less pressure and more time for family bonding, while worries about the pandemic, family health, and parenting challenges were also cited. Mental health concerns of breastfeeding women appear to be exacerbated by COVID-19, highlighting a critical need for access to mental health and broader family support during the pandemic.  相似文献   
150.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号